Professor Paul Lewis shared in supervising this project. This abstract is based on a senior project and paper; the results were also presented at the URICA Symposium, Bethel College, May 2, 2009. The present study is a cross-sectional study of the age-related development of cognition and how that is reflected in similarity judgments of music excerpts made by children, early adolescents and young adults. Four different participant age groups were used in this study: children from 5-7 years old, early adolescents from 8-11 and 12-16 years old, and young adults from 18-22 years old. Each participant in all four age groups made similarity judgments of music features in an original music excerpt and six other excerpts, chosen by aesthetic music search engine Armonique to be similar or dissimilar in pitch, rhythm and timbre from the original excerpt. The study found that for younger children before the formal operational cognitive stage, excerpts are rated lower on an increasing similarity scale, and significant results were gathered from the age and rating scale across groups, as well as qualitative differences in data obtained by asking different age groups about the music characteristics they use in making judgments. These results are coherent to empirical developmental studies and Piagetâ€™s cognitive theories.